UV-LIGA Microfabrication of a Power Relay
Based on Electrostatic Actuation
Ren Yang, Seok Jae Jeong, and Wanjun Wang
Department of Mechanical Engineering
Louisiana State University
Baton Rouge, LA 70810
USA
Louisiana State University
1.
2.
3.
4.
Introduction.
Design
Fabrication
Summary & Future work
1. Introduction
Different Types of Power Relays
1.
2.
3.
Traditional Relay
- Advantage: low on resistance, off-leakage, and big
output capacitance
- Disadvantage: large, noisy, slow, and difficult to
integrate
Solid-state Relay
- Advantage: much longer life time, fast response, low
noisy, smaller size
- Disadvantage: high on-resistance, low off-resistance,
high power consumption, and poor electrical
isolation
MEMS (Micro Electro Mechanical System) Relay
- Takes advantages from traditional and solid-state relay
General Principle Commonly Used MEMS Design

Electrostatic force

Magnetomotive force

Piezoelectrical force
2. Design
Schematic diagram of the micro power relay
Differences Compared to Other MEMS Relays

Not silicon based

Metal/Alloy as basic materials such as Ni
or Cu for conductivity

Thick metal/Alloy pads can be used instead
of thin metal films as silicon based relay
Fundamental calculation for electrostatic force
1
xq2
2
E
q 
2C
2A
P
dE
E dq
E dx


dt
q dt
x dt
V  i
 F v
F 
A
x
for a capacitor
E
1
A 2

q2 
e
x
2A
2x2
given data;
  8.85  10 12 F / m, A  2000 m
x  20 m, F  2.7656  10  7 N
 2x F
e  
 A

2




1
2
 ~ 25V
E:electrical energy stored by the capacitor
C: capacitance
P:power
q:current
x:gap
ε:electric permittivity of free space
E:voltage
A:surface area
3. Fabrication of micro-relay by UV-LIGA
What is UV-LIGA?
; Approach where a UV aligner is used with a thick
resist in place of the synchrotron x-ray exposure
step. After the lithography, electrodeposition and
planarization are used to produce metal micropart.
 Advantages
- High aspect-ratio microfabrication
- Broad selection of materials
- Slightly lower quality and much lower fabrication
cost compared to X-ray LIGA

Fabrication Method
Bottom part
Poles to support top part
3rd layer
Top part
15  m 2nd layer
Polymer connectors
Insulator to protect
short-circuit
1st layer
1st layer
Substrate (Si)
Assemble
Substrate (Si)
Bottom part
Electrodes to be
swithced on
Bottom capacitor for
electrostatic driving
Poles to support
top part
substrate
55 m
1st layer
photo resist(SU 8)
Substrate (Si)
Au/Cr seed layer
Electrodes to be
swithced on
Poles to support
top part
10 m
3rd layer
UV light
mask
1st layer
Substrate (Si)
Poles to support top part
3rd layer
15  m 2nd layer
developing
electroplating
metal structure
1st layer
Substrate (Si)
Top part
Suspension springs
Top capacitor plate
Switching connectors
1st layer
Substrate (Si)
Polymer connectors
Insulator to protect
short-circuit
substrate
photo resist
Au/Cr seed layer
UV light
mask
1st layer
Substrate (Si)
Insulation layer
Polymer connectors
Insulator to protect
short-circuit
developing
electroplating
metal structure
1st layer
Substrate (Si)
Separated structure
Top view picture of Bottom and top part
Side view schematic diagram of relay
polymer top plate
connector
polymer layer
suspension
spring
substrate
electorodes
Bottom part
Top part
bottom plate
supporting post
Initial open position
electrically isolated
deflection
substrate
electric connection made
Closing operation
Assembled top and bottom part
Adding an insulation layer on the bottom part
Top part
Bottom part
Electrodes to be
swithced on
Suspension springs
Bottom capacitor for Poles to support
electrostatic driving
top part
Top capacitor plate
Switching connectors
55 m
1st layer
Substrate (Si)
1st layer
Substrate (Si)
Electrodes to be
swithced on
Poles to support
top part
Polymer connectors
10 m
3rd layer
1st layer
Substrate (Si)
1st layer
Substrate (Si)
Poles to support top part
3rd layer
15  m
2nd layer
Insulation layer
1st layer
Substrate (Si)
Polymer connectors
1st layer
Substrate (Si)
Top view picture of Bottom and top part
Side view schematic diagram of relay
polymer top plate
connector
Insulation layer
suspension
spring
substrate
electorodes
Bottom part
Top part
bottom plate
supporting post
Initial open position
electrically isolated
deflection
substrate
electric connection made
Closing operation
Assembled top and bottom part
4. Preliminary test of assembled relay
Mechanical properties
Mass
Deflection
-7
6.0x10
Force (N)
Slope(K)=2.13*10
-3
-7
4.0x10
Slope(K)=1.75*10
-3
Measurement of deflection by applied weight
experiment
simulation
-7
2.0x10
-4
1.0x10
-4
2.0x10
Deflection (m)
-4
3.0x10
-4
4.0x10
Electrical properties
R=872kΩ
Experiment
Calculation
Working voltage
~10V
8.5V
Spring constant
1.7510-3N/
2.13103N/m
R=Infinite
I
4. Summary



Design of a novel micro-relay for power
applications based on electrostatic actuation
Fabrication by UV-LIGA
Preliminary test
 Control voltage: 10V
-3
 Spring constant: 1.7510 N/m
5. Future Work

Improve fabrication process



Measure physical properties



Low stress plating condition
Easy way separate top structure from the substrate.
Spring constant
Strength of polymer connector
Test working properties of the assembled power relay



On/off resistance
Life time
reliability